Galectin-3 binding protein (G3BP), also known as 90-kDa Mac-2 binding protein, was initially identified and characterized in breast cancer cells and in human milk [see, Koths K. et al. (1993) J. Biol. Chem. 268:14245-14249], and is a heavily N-glycosylated secreted protein of about 90 kDa. G3BP is known to interact with Galectin-3, Galectin-1 and Galectin-7 [see, Inohara et al. (1996) Cancer Research 56:4530-4534; Tinari, N. (2001) Int J Cancer 91:167-172; Liu, F T et al. (2005) Nat Rev Cancer 5:29-41]. Further, G3BP is elevated in the serum of subpopulations of patients with various types of cancer [see, Iacobelli S. et al. (1986) Cancer Res. 46:3005-3010; Iacobelli S. et al. (1988) Breast Cancer Res. Treat. 11:19-30; Iacobelli S. et al. (1994) Br. J. Cancer 69:172-176; Scambia, G. et al. (1988) Anticancer Res. 8:761-764], and in patients infected with human immunodeficiency virus (HIV) [see, Natoli et al. (1991) J. Infect. Dis. 164:616-617; Natoli et al. (1993) J. AIDS 6:370-375; Iacobelli, S. et al. (1991) J. Infect. Dis. 164:189; Briggs, N.C. et al. (1993) AIDS Res. Hum. Retroviruses; 9:811-816; Longo, G. et al. (1993) Br. J. Haematol. 85:207-209]. G3BP also has stimulatory effects on cells of the immune system, such as NK cells and lymphokine-activated killer cells [see, Ullrich, A. et al. (1994) J. Biol. Chem. 269:18401-18407]. A role for G3BP in inhibiting the spread of viruses within a host's body, however, has not been previously described.
While the immune system is designed to fight and, ideally, inhibit the spread of viral infection, certain viruses are especially adept at evading or overcoming the immune response. Moreover, immunocompromised individuals, such as those taking immunosuppressant drugs to prevent rejection of a transplanted organ, or those infected with HIV, are particularly susceptible to viral infection. While anti-viral medications are currently available for some viruses, many viruses rapidly mutate and become resistant to these drugs, and for other viruses, no such drugs are available [see, Barth R E et al. (2010), Lancet Infect Dis; 10:155-66; Marcelin A G et al. (2009), Curr Opin HIV AIDS; 4:531-537]. Therefore, new compositions and methods for preventing, delaying, or limiting the severity of viral infection in an individual are needed.
In the case of gene therapy, which is a technique for correcting a defective gene responsible for disease development by replacing or introducing mutations into the defective gene, it is actually desirable to enhance the spread of a virus (in the form of a vector) to organs and tissues. Specifically, viral vectors, such as those derived from adeno-associated virus (AAV), are commonly used to deliver a corrective gene to target tissues, and inhibiting or delaying the spread of such vectors to target tissues severely limits the efficacy of the vector. Currently, a number of vectors that would otherwise be useful for gene therapy, including AAV vectors in particular, are plagued by low efficiency, and methods for increasing their efficiency are needed.
AAV is an attractive candidate for generating viral vectors for gene therapy, because it is a small, single-stranded DNA virus that infects humans and certain other mammalian species, including dogs, but does not cause infection or elicit a strong host immune response. There are 11 known serotypes of AAV, AAV1-AAV11. AAV expresses the capsid proteins VP1, VP2 and VP3, which are involved in and are thought to be required for AAV infection of target tissues. The molecular weights of these proteins are 87, 72, and 62 kDa, respectively [Jay F T et al. (1981) PNAS; 78:2927-31]. Given the importance of capsid integrity on infectivity, all capsid proteins are likely required for infection. VP2 is especially important, as AAV capsid can only form in its presence [Ruffing et al. (1992) Journal of Virology; 66:6922-6930].
Clinical trials evaluating the safety and efficacy of AAV-vector based gene therapy for a broad variety of conditions are currently underway. These conditions include, for example, Pompe disease (caused by an acid alpha-glucosidase deficiency), inflammatory arthritis, Lebers Congenital Amaurosis (caused by RPE65 mutations), Canavan disease, childhood blindness (caused by mutations in RPE65), alpha 1-antitrypsin deficiency, heart failure, hemophilia, limb girdle muscular dystrophy type 2D, lipoprotein lipase deficiency, cystic fibrosis, Parkinson's disease, Duchenne muscular dystrophy, late infantile neuronal ceroid lipofuscinosis, Alzheimer's disease, and cutaneous B cell lymphoma [see, Journal of Gene Medicine website at http://www.wiley.co.uk/genetherapy/clinical/; http://www.abedia.com/wiley/images/0912vectors.jpg; Rodino-Klapac et al, Neurology (2008); 71:240-247; Towne et al, Gene Ther. (2010); 17: 141-146].
For effective use in gene therapy to treat conditions such as those described above, an AAV vector must achieve systemic distribution throughout target tissues (i.e., “tissue distribution”). One disadvantage of using AAV vectors for gene therapy is that many individuals are already seropositive for AAV. For instance, this value varies from 5% for AAV5 to 60% for AAV2 (these values are known for AAV1, 2, 5, 6, 8, 9) [see, Boutin et al., Hum Gene Ther. (2010) January 22. [Epub ahead of print]]. Serum antibodies in this population bind to and sequester AAV in the blood. The resultant antibody-AAV complexes are cleared by the liver, thereby preventing systemic distribution of the vector.
Even in gene therapy patients who are seronegative for AAV, however, efficiency of AAV penetration in target tissues is low, and high amounts of AAV vector must be administered to the patient in order for the dose of AAV to effectively achieve systemic distribution, including distribution into target tissues. The requirement for high concentrations of AAV vector poses a significant disadvantage for its use in gene therapy, since vector overloading can be toxic under certain circumstances. Furthermore, such high titres of vector can be difficult to produce. (See, Virag et al., Hum Gene Ther. (2009) 20:807-817).
As described above, there remains a need to identify methods and compositions for increasing the efficiency of AAV penetration into target tissues and to identify methods and compositions for inhibiting the spread of harmful viral infections. The present invention provides such methods and compositions.